The present invention relates generally to the field of wireless communications, and more specifically, to the field of noise and error removal from signals which are transmitted in an analog form and processed in digital form.
In wireless communications, data signals are typically transmitted through the air in an analog format, even if the signals were originally in a digital format. When a signal is transmitted, the signal can suffer interference from other signals being broadcast through the air, it can be blocked and/or reflected by large buildings and large natural objects, it can be subject to fading caused by moving objects temporarily blocking the transmission path between the source and the destination, etc. As a result from the above listed and other possible sources of interference, the analog signal as it arrives at the destination often includes noise and phase angle errors.
A typical method for removing injected noise and error from an analog signal and to convert it from analog mode back to digital mode is to simply pass the analog signal as it is received through a comparator, which will compare the analog signal against at least one decision threshold and, depending on the result of the comparison, will produce one of at least two output values. In typical applications where the analog signal is a simple representation of a binary signal, the comparator will have only one decision threshold. If the analog signal exceeds the threshold or thresholds, then the comparator will output a certain voltage value and if the analog signal is below the threshold or thresholds, then the comparator will output a different voltage value. While this method provides a quick and easy method for removing noise and error from the analog signal in addition to providing the conversion from analog to digital, it provides no information as to the probability that the received signal actually matches the original analog signal. Additionally, if the analog signal undergoes severe fading which results in the received signal dropping below the threshold level of the comparator, the output voltage of the comparator may be different from the transmitted analog signal.
There is, therefore, a need in the industry for a system addressing these and other related and unrelated problems.